The present application is an improvement over the foregoing applications and patent in that it is directed to a class of molecules that provides switching from one state to a different state, characterized by a change in the electrical conductivity.
1. Technical Field
The present invention relates generally to electronic devices whose functional length scales are measured in nanometers, and, more particularly, to classes of molecules that provide electronic switching. Electronic devices both of micrometer and nanometer scale may be constructed in accordance with the teachings herein.
2. Background Art
The area of molecular electronics is in its infancy. To date, there have been two convincing demonstrations of molecules as electronic switches published in the technical literature; see, C. P. Collier et al., Science, Vol. 285, pp. 391-394 (Jul. 16, 1999) and C. P. Collier et al., Science, Vol. 289, pp. 1172-1175 (Aug. 18, 2000), but there is a great deal of speculation and interest within the scientific community surrounding this topic. In the published work, a molecule called a rotaxane or a catenane was trapped between two metal electrodes and caused to switch from an ON state to an OFF state by the application of a positive bias across the molecule. The ON and OFF states differed in resistivity by about a factor of 100 and 5, respectively, for the rotaxane and catenane.
The primary problem with the rotaxane was that it is an irreversible switch. It can only be toggled once. Thus, it can be used in a programmable read-only memory (PROM), but not in a ROM-like device nor in a reconfigurable system, such as a defect-tolerant communications and logic network. In addition, the rotaxane requires an oxidation and/or reduction reaction to occur before the switch can be toggled. This requires the expenditure of a significant amount of energy to toggle the switch. In addition, the large and complex nature of rotaxanes and related compounds potentially makes the switching times of the molecules slow. The primary problems with the catenanes are small ON-to-OFF ratio and a slow switching time.
Thus, what is needed is a molecular system that avoids chemical oxidation and/or reduction, permits reasonably rapid switching from a first state to a second, is reversible to permit the fabrication of ROM like devices, and can be used in a variety of electronic devices.
In accordance with the present invention, a molecular system is provided for nanometer-scale reversible electronic switches, specifically, electric field activated molecular switches that have an electric field induced band gap change that occurs via a molecular conformation change or an isomerization. Changing of extended conjugation via chemical bonding change to change the band gap is accomplished by providing the molecular system with one rotating portion (rotor) and two stationary portions (stators), between which the rotor is attached.
The present invention provides nanometer-scale reversible electronic switches that can be assembled easily to make cross-bar and other circuits. The cross-bar circuits have been described in the above-listed series of patent applications and issued patent. The circuits provide memory, logic and communications functions. One example of the electronic switches is the so-called crossed-wire device, which comprises a pair of crossed wires that form a junction where one wire crosses another at an angle other than zero degrees and at least one connector species connecting the pair of crossed wires in the junction. The junction has a functional dimension in nanometers or larger for multilayers. The connector species comprises the molecular system disclosed and claimed herein.
The present invention introduces a new type of switching mechanism, namely, an electric field induced rotation of a rotatable middle section (rotor) of a molecule. Thus, the molecule is neither oxidized nor reduced in the toggling of the switch, which avoids the necessity of breaking chemical bonds and potentially initiating a nonreversible reaction. Also, the part of the molecule that moves is quite small, so the switching time should be very fast. Also, the molecules are much simpler and thus easier and cheaper to make than the rotaxanes and related compounds.
The devices of the present invention are generically considered to be electric field devices, and are to be distinguished from earlier embodiments (described in the above-mentioned related patent applications and patent) that are directed to electrochemical devices.
The molecular system of the present invention is expected to find use in a variety of applications, including, but not limited to, memories, logic devices, multiplexers, demultiplexers, configurable interconnects for integrated circuits, field-programmable gate arrays (FGPAs), cross-bar switches, and communication devices, such as cellular phones, mobile appliances, and PDAs.